/ 
Object-Util-0.010
River stage one • 2 direct dependents • 2 total dependents
/ Object::Util

NAME

Object::Util - a selection of utility methods that can be called on blessed objects

SYNOPSIS

use Object::Util;

# $foo might be undef, but this should not die
if ($foo->$_isa("Bar")) {
   ...;
}

DESCRIPTION

This module is inspired by Safe::Isa, Object::Tap, and my own OO experiences. It is a hopefully helpful set of methods for working with objects, exposed as lexical coderef variables.

Rationale

Providing methods as coderefs so that you can do:

$object->$_foo(@args)

... is unusual, so probably requires some explanation.

Firstly some of these methods are designed to be called on either a blessed object or some kind of unblessed reference or value. Calling a method on an unblessed reference like this will croak:

$ref->foo(@args)

Ditto calling methods on undef. Coderefs don't suffer from that problem.

More importantly though, the aim of this module is that these methods should be available for you to call on any object. You can only call $object->foo(@args) if $object's class implements a method called foo, or inherits from a superclass that does. Coderef methods can be called on any object.

This module adopts the $_foo naming convention pioneered by modules such as Safe::Isa. However (unlike Safe::Isa) the coderefs it provides are true lexical variables (a.k.a. my variables), not package variables (a.k.a. our variables).

Methods

Object construction and manipulation

$_new

Can be used like $class->$_new(@args) to create a new object. Object::Util will use Module::Runtime to attempt to load $class if it is not already loaded. $class is expected to provide a method called new.

Can also be used as $factory->$_new(@args) to create a new object, where $factory is a coderef or an object overloading &{}. In this case, $_new will simply call $factory->(@args) and expect that to return an object.

$_clone

If the object provides a clone method, calls that. Or if the object appears to be Moose- or Mouse-based, clones it using the metaobject protocol.

Otherwise takes the naive approach of treating the object as a hashref of attribute values, and creates a new object of the same class.

# clone overrides some attributes from the original object
my $glenda = $glen->$_clone(name => "Glenda", gender => "f");

That final fallback obviously massively breaks your class' encapsulation, so it should be used sparingly.

$_with_traits

Calling $class->$_with_traits(@traits) will return a new class name that does some extra traits. Should roughly support Moose, Mouse, Moo, and Role::Tiny, though combinations of frameworks (e.g. consuming a Moose role in a Mouse class) will not always work.

If $class is actually a (factory) coderef, then this will only partly work. Example:

my $factory  = sub { Foo->new(@_) };
my $instance = $factory->$_with_traits("Bar")->$_new(%args);

The object $instance should now be a Foo object, and should do the Bar role, however if Bar defines any attributes, then $_new will not have initialized them correctly. This is because of the opacity of the $factory: $_with_traits cannot peek inside it and apply traits to the Foo class; instead it needs to build $instance and apply the traits to the already-built object. Therefore any behaviour that Bar defines for the constructor will have been ignored.

It is sometimes possible to work around this issue using:

my $factory  = sub { Foo->new(@_) };
my $instance = $factory->$_with_traits("Bar")->$_new(%args);
$instance = $instance->$_clone(%args);
$_extend

Calling $object->$_extend(\@traits, \%methods) will add some extra roles and/or methods to an existing object.

Either @traits or %methods may be omitted. That is, $object->$_extend(\@traits) will add some traits to an existing object but no new methods, and $object->$_extend(\%methods) will add new methods, but no traits. $object->$_extend() also works fine, and is a no-op.

This method always returns $object, which makes it suitable for chaining.

Like Object::Extend, but with added support for roles.

$_murder

Called on an object, tries its best to destroy the object.

my $object = Foo->new;
$object->$_murder;
defined($object);   # false

Not only will $object be set to undef in the above example, but if there were any other references to the object, $_murder will do its best to poison them too.

$_murder will empty out the contents of the underlying hash or array in hashref-based and arrayref-based objects, and for scalarref-based objects will set the underlying scalar to undef.

$_murder will also rebless the reference into a dummy class where all method calls will croak.

$_murder will generously ensure that the object's DESTROY is called before initiating the killing spree, allowing the class to perform any necessary clean-up first.

Method call modifiers

$_call_if_object

$object->$_call_if_object($method => @args) works like $object->$method(@args), but if $object is undefined, returns undef instead of throwing an exception.

$method may be a method name, or a coderef (anonymous method).

Same as Safe::Isa.

$_try

$object->$_try($method => @args) works like $object->$method(@args), but if any exception is thrown returns undef instead.

$method may be a method name, or a coderef (anonymous method).

$_tap

$object->$_tap($method => @args) works like $object->$method(@args), but discards the method's return value (indeed it calls the method in void context), and instead returns the object itself, making it useful for chaining.

$method may be a method name, or a coderef (anonymous method).

Same as Object::Tap, or the tap method in Ruby.

$_isa

$object->$_isa($class) works like isa as defined in UNIVERSAL, but if $object is undefined, returns false instead of throwing an exception.

A shortcut for $object->$_call_if_object(isa => $class).

Same as Safe::Isa.

$_does

$object->$_does($role) works like does as defined in Moose::Object, but if $object is undefined, returns false instead of throwing an exception.

A shortcut for $object->$_call_if_object(does => $role).

Same as Safe::Isa.

$_DOES

$object->$_DOES($role) works like DOES as defined in UNIVERSAL, but if $object is undefined, returns false instead of throwing an exception.

A shortcut for $object->$_call_if_object(DOES => $role).

Same as Safe::Isa.

$_can

$object->$_can($method) works like can as defined in UNIVERSAL, but if $object is undefined, returns undef instead of throwing an exception.

There is one other significant deviation from the behaviour of UNIVERSAL's can method: $_can also returns true if $method is an unblessed coderef. (The behaviour of $method if it is a blessed object -- particularly in the face of overloading -- can be unintuitive, so is not supported by $_can.)

Similar to Safe::Isa, but not quite the same.

Object utility methods

$_dump

Calling $object->$_dump returns a Data::Dumper dump of the object, with some useful changes to the default Data::Dumper output. (Same as Data::Dumper::Concise.)

If the object provides its own dump method, this will be called instead. Any additional arguments will be passed through to it.

$_dwarn

Calling $object->$_dwarn(@args) prints a similar dump of the object and any arguments as a warning, then returns the object, so is suitable for tap-like chaining.

Unlike $_dump, will not call the object's own dump method.

$_dwarn_call

Calling $object->$_dwarn_call($method, @args) calls the method on the object, passing it the arguments, and returns the result. Along the way, it will dump the object, method, arguments, and return value as warnings. Returns the method's return value.

Unlike $_dump, will not call the object's own dump method.

Implementation Details

B::Hooks::Parser is used to inject these methods into your lexical scope, and Internals::SvREADONLY (an internal function built into the Perl core) is used to make them read-only, so you can't do:

use Object::Util;
$_isa = sub { "something else" };

If this module detects that B::Hooks::Parser cannot be used on your version of Perl, or your Perl is too old to have Internals::SvREADONLY, then it has various fallback routes, but the variables it provides may end up as package (our) variables, or not be read-only.

If the magic works on your version of Perl, but you wish to avoid the magic anyway, you can switch it off:

use Object::Util magic => 0;

The magic may trigger bugs if you're loading Object::Util in a sufficiently unusual way (for example, require and import instead of use). If this happens, disable magic.

BUGS

Please report any bugs to http://rt.cpan.org/Dist/Display.html?Queue=Object-Util.

SEE ALSO

Safe::Isa, UNIVERSAL, Object::Tap, MooseX::Clone, Data::Dumper::Concise, Object::Extend.

AUTHOR

Toby Inkster <tobyink@cpan.org>.

COPYRIGHT AND LICENCE

This software is copyright (c) 2014, 2018 by Toby Inkster.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

DISCLAIMER OF WARRANTIES

THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.